No, it's because when you do SS (a weightlifting program for beginners) it stresses the main compound lifts which are squats, deadlifts, bench press, and overhead press. And the first few months that people do this, they put on a LOT of weight. Since the muscles in the legs and back are the biggest, they gain weight the fastest. It takes a good few months after those beginner stages to even out the upper body with the lower.

I'm actually doing SS right now, I'm precisely a month in (first time I went was Feb 5th). I'm slowly on my way to centaur mode